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arXiv:2401.17454 · Applied Physics Letters

Frequency-domain multiplexing of SNSPDs with tunable superconducting resonators

Sasha Sypkens, Lorenzo Minutolo, Sahil J. Patel, Emanuel Knehr, Alexander B. Walter, Henry George LeDuc, Lautaro Narváez, Ralph V. Chamberlin, Tracee Jamison-Hooks, Matthew D. Shaw, Peter K. Day, Boris A. Korzh

Published Jun 24, 2024• 8 citations
arXivHTMLPDF

Abstract

This work culminates in a demonstration of an alternative frequency-domain multiplexing (FDM) scheme for superconducting nanowire single-photon detectors (SNSPDs) using the kinetic inductance parametric up-converter (KPUP) made out of NbTiN. There are multiple multiplexing architectures for SNSPDs that are already in use, but FDM could prove superior in applications where the operational bias currents are very low, especially for mid-infrared and far-infrared SNSPDs. Previous FDM schemes integrated the SNSPD within the resonator, while, in this work, we use an external resonator, which gives more flexibility to optimize the SNSPD architecture. The KPUP is a DC-biased superconducting λ/2 resonator that is sensitive to current perturbations. When coupled to an SNSPD, the KPUP can be used to read out current pulses on a few μA scale. The KPUP is made out of NbTiN, which has a large kinetic inductance and a high operating temperature. Meanwhile, the SNSPD is made from WSi, which is a popular material for broadband SNSPDs. A software-defined radio platform and a graphics processing unit are used to read out the KPUP and SNSPD array. Frequency-domain multiplexed SNSPDs have applications in astronomy, remote sensing, exoplanet science, dark matter detection, and quantum sensing.

DOI
10.1063/5.0220090

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This work culminates in a demonstration of an alternative frequency-domain multiplexing (FDM) scheme for superconducting nanowire single-photon detectors (SNSPDs) using the kinetic inductance parametric up-converter (KPUP) made out of NbTiN. There are multiple multiplexing architectures for SNSPDs that are already in use, but FDM could prove superior in applications where the operational bias currents are very low, especially for mid-infrared and far-infrared SNSPDs. Previous FDM schemes integrated the SNSPD within the resonator, while, in this work, we use an external resonator, which gives more flexibility to optimize the SNSPD architecture. The KPUP is a DC-biased superconducting λ/2 resonator that is sensitive to current perturbations. When coupled to an SNSPD, the KPUP can be used to read out current pulses on a few μA scale. The KPUP is made out of NbTiN, which has a large kinetic inductance and a high operating temperature. Meanwhile, the SNSPD is made from WSi, which is a popular material for broadband SNSPDs. A software-defined radio platform and a graphics processing unit are used to read out the KPUP and SNSPD array. Frequency-domain multiplexed SNSPDs have applications in astronomy, remote sensing, exoplanet science, dark matter detection, and quantum sensing.
Single photon detection advanced rapidly in the last decade. The superconducting nanowire single-photon detector (SNSPD) is an emerging technology, which offers low dark count rates, broadband sensitivity from visible to mid-infrared wavelengths and very high quantum efficiency. All these features are appealing for future emerging applications in remote gas sensing, quantum key distribution and quantum information processing. By enclosing the detector in an optical cavity, tuned to the operating wavelength, the total system detection of the SNSPD is improved. Based on the cavity design, the detector absorption is boosted at the desired experimental wavelength. Devices have been fabricated and tested, in this thesis, with enhanced detection efficiency at near-infrared, infrared and mid-infrared wavelengths. NbTiN detectors fabricated on Ta2O5 / SiO2 distributed Bragg reflectors (DBR) for front-side coupling exhibit a system detection efficiency of ≈ 90% at λ = 940 nm for the best device measured. SNSPDs were also fabricated in NbTiN on metallic mirrors for back-side coupling for 1550 and 2333 nm experimental wavelengths. The first design exhibited a system detection efficiency of ≈ 84.5%, at λ = 1550 nm for the best device measured. The second exhibited low system detection efficiency since the device suffered from unexpectedly high dark count rate mainly due to blackbody radiation at 2.2 K. However, it was possible to measure the timing jitter of this device at 350 mK indicating a FWHM of 84 ps. Another technique to improve the total system detection efficiency of the SNSPD, is by fabricating a hairpin-shaped nanowire atop a single mode waveguide. In this design, photons travel through the waveguide and via evanescent coupling are absorbed in the nanowire. These SNSPD devices have been designed to thread along single mode Si ridge waveguides using a hairpin-shaped nanowire structure, which offers enhanced coupling and absorption efficiency via evanescent coupling. These ultra-thin superconducting MoSi detectors are precisely patterned on top of a single mode Si waveguide (600 nm) with alignment error less than 40 nm. Low temperature electrical and nano-optical characterization was carried out using a two-stage pulse tube (PT) coldhead, using an additional 4He / 3He sorption pump, low vibration characterization of SNSPD devices at 350 mK was carried out. Characterised devices exhibit low dark count rate <5 counts per second and timing jitter of ≈ 83 ps full width half maximum (FWHM) at wavelength (λ) = 1550 nm and at critical current ≈ 30 µA.
Superconducting nanowires are widely used as sensitive single photon detectors with wide spectral coverage and high timing resolution. We describe a demonstration of an array of dc-biased superconducting nanowire single photon detectors read out with a microwave multiplexing circuit. In this design, each individual nanowire is part of a resonant LC circuit where the inductance is dominated by the kinetic inductance of the nanowire. The circuit also contains two parallel plate capacitors, one of them is in parallel with the inductor and the other is coupled to a microwave transmission line that carries the signals to a cryogenic low-noise amplifier. All of the nanowires are connected via resistors to a single dc bias line that enables the nanowires to be current biased close to their critical current. When a photon hits a nanowire, it creates a normal hotspot that produces a voltage pulse across the LC circuit. This pulse rings down at the resonant frequency of the LC circuit over a time period that is fixed by the quality factor. We present measurements of an array of these devices and an evaluation of their performance in terms of frequency and time response.
We fabricated superconducting nanowire single-photon detectors (SNSPDs) made of NbTiN and NbN thin films in the same fabrication batch. Various parameters, such as critical temperature, resistivity, switching current, and kinetic inductance, were compared between the two types of SNSPDs. These data indicate that NbTiN SNSPD surpasses NbN SNSPD in many aspects, including a shorter recovery time due to smaller kinetic inductance, a lower timing jitter due to higher switching current, and better uniformity. Based on the measurement of 28 out of 121 NbTiN SNSPDs on a 2-in Si wafer, 71% of detectors show a system detection efficiency of over 50% at a dark count rate of 100 Hz, with the maximum efficiency being 77.5%.
Abstract Superconducting nanowire single-photon detectors (SNSPDs) have become increasingly important for both classical and quantum applications requiring single-photon sensing. Most current SNSPDs based on superconducting niobium nitride (NbN) ultrathin films are fabricated utilizing polycrystalline or amorphous superconductor films, and film inhomogeneity and defectivity can cause significant issues. Here, we present an all-epitaxial approach for fabricating SNSPDs with integrated metal reflectors, semiconductor (dielectric) resonators, and superconductor nanowire detectors. A working example is realized by molecular-beam epitaxy growth of a tri-layered heterostructure, consisting of a titanium nitride (TiN) reflector with ~ 92% reflectivity at the telecommunication wavelength (1550 nm), an aluminum nitride (AlN) resonator with a broad optical transparency window, and a NbN nanowire on c -plane sapphire wafer. The all-epitaxial approach provides a manufacturable platform with superior material properties, as well as uniformity across the wafer, which manifest themselves in tunable material parameters of the superconducting nanowire, including normal-state resistance, superconducting critical temperature, superconducting critical current, and kinetic inductance. The optimized material properties can be utilized to achieve excellent SNSPD performance, including wafer-scale uniformity in device characteristics and broadband (~300 nm) system detection efficiency (>90%) centered at 1550 nm, suitable for large-scale detector arrays and wavelength-division multiplexing (WDM) applications.
© 2002-2011 IEEE. Superconducting nanowires are widely used as sensitive single photon detectors with wide spectral coverage and high timing resolution. We describe a demonstration of an array of dc-biased superconducting nanowire single photon detectors read out with a microwave multiplexing circuit. In this design, each individual nanowire is part of a resonant LC circuit where the inductance is dominated by the kinetic inductance of the nanowire. The circuit also contains two parallel plate capacitors, one of them is in parallel with the inductor and the other is coupled to a microwave transmission line that carries the signals to a cryogenic low-noise amplifier. All of the nanowires are connected via resistors to a single dc bias line that enables the nanowires to be current biased close to their critical current. When a photon hits a nanowire, it creates a normal hotspot that produces a voltage pulse across the LC circuit. This pulse rings down at the resonant frequency of the LC circuit over a time period that is fixed by the quality factor. We present measurements of an array of these devices and an evaluation of their performance in terms of frequency and time response.
Superconducting nanowire single-photon detectors (SNSPDs) in the mid-infrared (MIR) have the potential to open up numerous opportunities in fields such as exoplanet searches, direct dark matter detection, physical chemistry, and remote sensing. One challenge in pushing SNSPD sensitivity to the MIR is a decrease in the signal-to-noise ratio (SNR) of the readout signal, as the critical currents become increasingly smaller. We overcome this trade-off with a device architecture that employs impedance matching tapers and superconducting nanowire avalanche photodetectors to demonstrate increased SNR while maintaining saturated internal detection efficiency at 7.4 μm and approaching saturation at 10.6 μm. This work provides a platform for pushing SNSPD sensitivity to longer wavelengths while enabling the scalability to large arrays.